This invention relates to a door structure and a method for forming such structure and more particularly to an improved door structure suitable for use as garage door panels.
In the past, garage doors have been manufactured from various materials including steel, glass fiber reinforced plastic and wood products. A typical garage door includes a plurality of elongated rectangular door panels which are attached to a track by means of rollers for opening and closing in a vertical direction. The panels extend the width of the door, for example, sixteen feet for a two car garage, are each one to two feet high and are generally one to two inches in thickness. Steel door panels may have only a single thickness of metal with a reinforcement frame extending around the periphery of each panel. Glass fiber reinforced plastic panels were commonly formed of a single thickness of plastic having horizontally extending corrugations for strength. Wooden doors have been constructed from either individual boards or from a hardboard such as Masonite laminated to both sides of a hollow wooden frame. In recent times, the hollow hardboard door construction has been most popular for new home construction. However, several problems are inherent in this type of door. Since garage doors are exposed to the weather, moisture can eventually penetrate the door panels and cause the hardboard to delaminate. Furthermore, the door panels for larger doors tend to sag or warp under the weight of the panel. This requires the addition of steel reinforcement channels along the back of each panel. However, the reinforcement channels in turn add to the cost of the door panels and further increase the total weight of the door which in turn requires heavier hardware, such as heavier counterbalance springs and heavier tracks for mounting the door. Furthermore, the door panels do not lend themselves to decoration without requiring additional labor during manufacture. Still another problem exists in prior art hardboard door panels in obtaining a weathertight seal between adjacent panels when the door is closed. The seal must be of a design which permits the panels to separate with respect to one another as the door is opened. Typical prior art hardboard door panels incorporate a shiplap type construction to form a weather seal.
Doors have been manufactured with a molded covering, such as a molded polyurethane, over a honeycomb core. Such a door structure is shown, for example, in U.S. Pat. No. 3,753,843 which issued Aug. 11, 1973. However, this construction has lacked the rigidity required for long garage door panels. When such panels were used in garage doors, the panels would sag, particularly when the door was left in a raised position with the panels extending horizontally. Twisting and sag detracted from the appearance of the door and prevented forming an acceptable seal between adjacent panels and between the panels and a door frame when the door was closed. Twisting is particularly bad in cold climates where the two sides of a door are subjected to a large temperature differential.